1. Field of the Invention
The present invention relates to a drive wave generation circuit which generates two types of drive waves for driving a piezo actuator.
2. Description of the Related Art
Piezo actuators employing elongation and contraction of a piezo element have been proposed, and have gained attention as ultra-small actuators (KONICA MINOLTA TECHNOLOGY REPORT Vol. 1 (2004), p. 23-26). Such piezo actuators are employed in a device such as cameras which include, for example, a mechanism which drives the image capturing element in order to compensate for shaking of the camera when held by hand, or in a focusing mechanism that moves the camera lens.
In a piezo actuator, a voltage is applied to a piezo element (piezoelectric element) so as to cause elongation and contraction of the element, thereby generating a reciprocating movement of a drive shaft. By configuring such that the moving speed of the drive shaft in one direction differs from the moving speed in the opposite direction (i.e., by causing slow elongation and quick contraction, or vice versa), it is possible to cause movement of a movable object placed in frictional contact with the drive shaft. By employing the elongation and contraction of a piezo element as the drive force, linear movement of an object can be achieved without using coils or the like, making it possible to downsize actuators.
In order to change the moving speed of the drive shaft, voltage waveforms applied to the piezo element must be changed. For example, in order to cause slow elongation and quick contraction, it is necessary to perform voltage application in a pattern in which voltage in a first direction is applied slowly and then voltage in the opposite direction is applied abruptly.
When moving an object such as a lens in a manner as described above using a piezo actuator, reciprocating movement of a drive shaft is caused, and the movable object such as a lens is made to slide with respect to the drive shaft. Accordingly, the absolute position of the lens cannot be determined without providing a lens position detector. Meanwhile, for cameras mounted on a cellular phone or the like, any reduction in size or cost is very desirable.